This invention relates to the priming of explosive devices, more particularly rimfire cartridges, for example 0.22 rimfire cartridges.
By far the most common method of priming rimfire cartridges comprises dosing a predetermined amount of wet priming composition into respective, empty rimfire cartridge cases and then forcing the wet priming composition into the rim of each case using a rapidly rotating so-called "spinning punch". The cases are then passed to an oven in which the priming composition is dried and they are subsequently loaded with propellant and, in the case of live rounds, bulleted. That method has been practised for many years and is well-known to those skilled in the art. An alternative well-known but less commonly used method is that known as "dry heading". Both methods are extremely hazardous, inter alia, because they involve the handling, either wet or dry depending on the method used, of bulk primary explosives, for example lead styphnate, and of bulk priming compositions containing such primary explosives. The spinning process, too, has its disadvantages, particularly cost disadvantages, as it is necessary frequently to replace the punches because they wear rapidly.
In our British Pat. No. 1 569 874 the disclosure of which is incorporated herein by reference, we describe and claim a method of substantially mitigating the hazards of priming explosive devices, including rimfire cartridges. In that specification, we describe, inter alia, an improved, relatively safe method of priming rimfire cartridges comprising the steps of (a) dosing an amount of a substantially dry, relatively insensitive, premix into each, empty, cartridge case, the premix containing components that will, in the presence of a liquid reaction medium such as water, react together forming a highly sensitive primary explosive compound and further containing one or more ingredients intended to form part of the priming composition, (b) dosing a quantity of said liquid reaction medium into each case whereupon the said components react forming the primary explosive compound, (c) forcing at least some of the resulting wet priming composition into the cartridge rims and (d) drying the composition. Step (b) may be carried out before step (a), although it is preferred first to dose the premix into the cases followed by addition of the liquid reaction medium. By way of example, the premix may contain in predetermined quantities, as said components, styphnic acid and lead oxide which, in the presence of water as the reaction medium, react forming lead styphnate and, as said ingredients, an oxidiser such as bariumnitrate, a small proportion of sensitiser such as tetrazene and a frictionator such as powdered glass. Conveniently the premix may be made up in relatively large batches followed by dosing thereof into the cases and because it is relatively insensitive (because it does not contain lead styphnate as do the compositions usually used in conventional priming processes), it can be safely handled in bulk even though dry. This means, in particular, that the actual step of providing the priming composition in the case before spinning can be carried out using automated machinery which, in the conventional priming methods is not practically possible because of the dangers involved in handling bulk priming compositions. By way of explanation the sensitivity mentioned above and hereinafter in relation to the premix refers to the tendency of the whole of a substantially unconfined mass thereof to explode or rapidly deflagrate as a result of application of heat, friction, shock or electrostatic sparks to any part of the mass. Thus, the premix should have relatively little, or no, such tendency particularly when handled, either by hand or machinery, under normal factory conditions compared with certain primary explosive compounds such as lead styphnate, and compositions containing them, which have a very high such tendency, especially when dry.
The dry premix may, however, contain small amounts, for example up to 10%, of certain sensitive materials such as tetrazene which, although dangerous when dry and substantially unadulterated are sufficiently diluted by other relatively insensitive materials of the premix that the premix is safe to handle in bulk.
Steps (c) and (d) mentioned above are, as has already been indicated, conventional in the art and step (c) entails the use of conventional spinning with the inherent disadvantages mentioned above.
It is an object of the present invention to improve the method described in our above-identified earlier specification, in so far as it relates to the priming of rimfire cartridges. In particular it is an object of the invention to obviate the need to use high speed rotating spinning punches for forcing the priming composition into the rims of rimfire cartridge cases.